std::stod, std::stof, std::stold in C++

1. std::stod() : It convert string into double.
   Syntax:

   double stod( const std::string& str, std::size_t* pos = 0 );
   double stod( const std::wstring& str, std::size_t* pos = 0 );
   Return Value: return a value of type double
   Parameters
   str : the string to convert
   pos : address of an integer to store the 
   number of characters processed. This parameter can also be 
   a null pointer, in which case it is not used.
   

   // CPP program to illustrate
   // std::stod()
   #include <string>
   #include <iostream>
   
   int main(void)
   
   {
       std::string str = "y=4.4786754x+5.6";
   
       double y, x, a, b;
       y = 0;
       x = 0;
   
       // offset will be set to the length of
       // characters of the "value" - 1.
       std::size_t offset = 0;
   
       a = std::stod(&str[2], &offset);
       b = std::stod(&str[offset + 3]);
   
       std::cout << b;
       return 0;
   }

   Output:

   5.6
   

   Another Example :

   // CPP program to illustrate
   // std::stod()
   #include <iostream>
   #include <string>
   using namespace std;
   int main()
   {
   
       string b = "5";
       double a = stod(b);
       int c = stoi(b);
       cout << b << " " << a << " " << c << endl;
   }

   Output:

   5 5 5
   

   If conversion is not performed, an invalid_argument exception is thrown. If the value read is out of the range of representable values by a double an out_of_range exception is thrown. An invalid idx causes undefined behavior.

2. std::stof : It convert string into float.
   Syntax:

   float stof( const string& str, size_t* pos = 0 );
   float stof( const wstring& str, size_t* pos = 0 );
   Parameters
   str : the string to convert
   pos : address of an integer to store the number of characters processed
   This parameter can also be a null pointer, in which case it is not used.
   Return value: it returns value of type float.

   Example 1:

   // CPP program to illustrate
   // std::stof()
   #include <iostream>
   #include <string>
   int main()
   {
       std::string x;
       x = "20";
       float y = std::stof(x) + 2.5;
       std::cout << y;
       return 0;
   }

   Output:

   22.5
   

   Example 2:

   // CPP program to illustrate
   // std::stof()
   #include <iostream>
   #include <string>
   int main()
   {
       std::string str = "5000.5";
       float x = std::stof(str);
       std::cout << x;
       return 0;
   }

   Output:

   5000.5
   

   If no conversion could be performed, an invalid_argument exception is thrown.

3. std::stold : It convert string into long double.
   Syntax:

   long double stold( const string& str, size_t *pos = 0 );
   long double stold (const wstring& str, size_t* pos = 0);
   Parameters : 
   str : the string to convert
   pos : address of integer to store the index of the first unconverted character.
   This parameter can also be a null pointer, in which case it is not used.
   Return value : it returns value of type long double.
   

   Examples 1:

   // CPP program to illustrate
   // std::stold()
   #include <iostream>
   #include <string>
   int main()
   {
       std::string str = "500087";
       long double x = std::stold(str);
       std::cout << x;
       return 0;
   }

   Output:

   500087
   

   Example 2:

   // CPP program to illustrate
   // std::stold()
   #include <iostream>
   #include <string>
   int main()
   {
       std::string x;
       x = "2075";
       long double y = std::stof(x) + 2.5;
       std::cout << y;
       return 0;
   }

   Output:

   2077.5